Detecting if a link is internal and shorten it accordingly

I have been thinking about making a helper method that shortens internal links. For example: if my website is example.com and a user posts a link to http://www.example.com/posts/80 it would be nice to shorten the link text to post#80 and http://www.example.com/comments/5 to comment#5.

would this su开发者_高级运维ffice

url["http://www.example.com/posts/"] = "post#"

Or should I use a regex for this instead?

regexp!

SITE_URL = 'http://www.example.com'    # make sure there is no trailing slash /

url = "http://www.example.com/posts/80"

short_url = url.sub( %r{^#{SITE_URL}(.*)$} , '\1')
  => "/posts/80"